HEMT having conduction barrier between drain fingertip and source

Abstract

A High Electron Mobility Transistor (HEMT) includes an active layer on a substrate, and a Group IIIA-N barrier layer on the active layer. An isolation region is through the barrier layer to provide at least one isolated active area including the barrier layer on the active layer. A gate is over the barrier layer. A drain includes at least one drain finger including a fingertip having a drain contact extending into the barrier layer to contact to the active layer and a source having a source contact extending into the barrier layer to contact to the active layer. The source forms a loop that encircles the drain. The isolation region includes a portion positioned between the source and drain contact so that there is a conduction barrier in a length direction between the drain contact of the fingertip and the source.

The invention claimed is: 
     
       1. A method of forming a High Electron Mobility Transistor (HEMT), comprising:
 providing a substrate; 
 forming a Group IIIA-N active layer on said substrate; 
 forming a Group IIIA-N barrier layer on said active layer; 
 forming at least one isolation region through said barrier layer to provide at least one isolated active area comprising said barrier layer on said active layer; 
 forming a gate over said barrier layer; 
 forming a drain comprising at least one drain finger including a fingertip having a drain contact extending into said barrier layer to provide contact to said active layer, and 
 forming a source having a source contact extending into said barrier layer to provide contact to said active layer, wherein said source forms a loop that encircles said drain, 
 wherein said isolation region includes a portion positioned between said source and said drain contact so that there is a conduction barrier in a length direction of said drain finger between said drain contact of said fingertip (drain contact fingertip) and said source. 
 
     
     
       2. The method of  claim 1 , wherein said fingertip is a curved region, and wherein said conduction barrier blocks conduction through at least a 150 degree arc in a path from said source to said drain contact fingertip. 
     
     
       3. The method of  claim 1 , wherein said forming said isolation region comprises a Mesa etch process that etches through said barrier layer. 
     
     
       4. The method of  claim 3 , wherein said forming said isolation region comprises patterning using a greyscale mask so that said Mesa etch process provides rounded edges for edges of said isolated active area. 
     
     
       5. The method of  claim 1 , wherein said forming said isolation region comprises a masked ion implantation process. 
     
     
       6. The method of  claim 1 , further comprising forming at least one buffer layer on said substrate before forming said Group IIIA-N active layer, wherein said substrate comprises silicon, wherein said Group IIIA-N active layer comprises undoped GaN, and wherein said barrier layer comprises AlGaN. 
     
     
       7. The method of  claim 1 , wherein said drain contact extends beyond said source contact. 
     
     
       8. The method of  claim 1 , wherein said HEMT is part of an integrated circuit (IC) formed in and on said substrate.